Method of separating pyrrhotite from chalcopyrite and gangue.



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JOHN N. JUDSON, OF SOUTH STRAFFORD, VERMONT.

METHOD OF SEPARATING PYRRHOTITE FROM CHALCOPYRITE AND GANGUE.

Specification of Letters Patent.

Patented Oct. 17, 1905.

Application filed July 22, 1905. Serial No. 270,864.

10 (MA wlwm, it may concern.-

Be it known that 1, JOHN N. JUDsoN, a citizen of the United States, residing at South Straiford, county of Orange, State of Vermont, have invented certain new and useful Improvements in Methods of Separating Pyrrhotite from Ohalcopyrite and Gangue; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to a certain new and useful method for the treatment of ores containing non-magnetic or weakly-magnetic varieties of the mineral pyrrhotite associated with the copper mineral chalcopyrite and the usual gangue minerals found in such ores-as, for instance, garnets, mica, feldspar, quartz, and the like.

The main object of my invention is to effect the concentration of the copper contents of the ore in the gangue minerals. This concentration of the copper contents of the ore in the gangue gives a product from which the copper can be more readily obtained by wellknown concentrating or metallurgical methods than it can be from the crude ore. The concentration contemplated by my invention involves the removal of the pyrrhotite from the ore,and consequently the mechanical elimination of the far greater part of the sulfur in the ore, which under the present method of treating such ores is discharged into the atmosphere as sulfurous oxid gas, to the destruction of vegetation and the annoyance of the communities in which the operations are carried on.

Another object of my invention is to remove the pyrrhotite from the ore so free from gangue and in such a relatively pure state that it will run high enough in sulfur to be commercially available for the manufacture of sulfuric acid.

Pyrrhotite is usually so highly magnetic that it can be removed from most ores containing it without difiiculty by the aid of almost any kind of a magnetic separator. Certain kinds of pyrrhotite, however, are practically non-magnetic or so weakly magnetic as to be incapable of attraction in their native condition by any of the usual types of magnetic separators. For instance, at Copperfield and at South Strafl'ord, Vermont, and at certain places in Virginia the pyrrhotite contained in the ore deposits is so weakly magnetic that while it can possiblybe removed to some degree by the most powerful magnets employed in separators of the kind known commercially as the Rowand type IE it is at so slow a rate that the commercial employment of such aseparator is out of the question. The separation of the pyrrhotite from the chalcopyrite of these ore deposits by any of the usual air-jigging or water-jigging methods'is not possible because of the fact that the specific gravity of pyrrhotite is substantially the same as the specific gravity of chalcopyrite. In investigating experimentally the treatment of these complex ores for the purpose of separating the non-magnetic or weaklymagnetic pyrrhotite therefrom l have discovered that if the ores are crushed to the proper degree of fineness say to a size sufficient to pass through a No. 10 screen or to a still finer sizeand are then heated slightly each particle of pyrrhotite acquires a bornite-like iridescence or surface film of rainbow colors (probably due to an incipient oxidation on the surface) and that the particles then become much more permeable to the magnetic lines of force, and consequently more readily susceptible to magnetic attraction. Forinstance, (where such pyrrhotite could not be removed by a Rowand two-magnet separator of the E type, excited by forty-five amperes'of current, at a rate to exceed three hundred to four hundred pounds per hour,) after receiving the surface film referred to a single Rowand magnet of the same construction excited with a current of six amperes would treat the same ore at the rate of two tons per hour, making a most excellent separation. The same separator excited by the same amount of current would not remove the pyrrhotite from crude or untarnished ore. The great economy in the cost of the plant and in the electrical energy necessary to operate it effected by treating the ore after its magnetic permeability has been increased in the manner indicated and also the greater amount of output per hour for each individual separator renders the treatment of the ore by the method incident to the practice of my present invention economically possible.

The range of temperatures through which the changes indicated may be effected is con siderable, but, nevertheless, limited. The ore must not be allowed to reach a red heat, for that would render the chalcopyrite magnetic also, and, on the other hand, it should, at the lower limits incident to successful practice, be rather too hot to hold in ones hand.

' each piece of pyrrhotite magnetic.

If the iridescence or film of colors hereinbefore referred to as observable upon the particles of pyrrhotite treated in accordance With my invention is, in fact, due to incipient surface exidation, itWould seem evident that some of the sulfur of the pyrrhotite must have been driven ofi in the operation; but in any event the amount thus driven off must be small, inasmuch as the separated pyrrhotite usually contains about thirty-three per cent. of sulfur and only a faint odor of sulfurous oXid is noticeable during the operation.

In the practice of my inventi0nsay, for instance, for the separation of the pyrrhotite from the chalcopyrite of the ores at the Elizabeth mine, South Strafford, Vermontthe ore Will first be roughly crushed in a Blake rock-crusher and then further reduced by rolls to pieces of about fivc-eighths of an inch in thickness. This crushed ore Will then be heated in a suitable furnace to the proper degree necessary to render the outer surface of The ore is then removed from the furnace and is screened upon a No. lO-mesh screen. The portion Which passes through the meshes of the No. lO-mesh screen is sent to the magnetic separator for the removal of the pyrrhotite noW rendered magnetic. The oversize, or portion Which does not pass through the screen, is then crushed to such a degree as to pass through a No. 10-mesh screen and is returned to the heating-furnace, so as to insure that the pyrrhotite in the interior of the oversize lumps shall be ultimately rendered mag netic. From the furnace such retreated material Will again pass through the screen and to the magnetic separators for the removal of the pyrrhotite, as above stated. The residue remaining after the pyrrhotite has been removed by the magnetic separators is to be roasted for the oxidation of the iron of the chalcopyrite and other sulfur minerals present in any suitable roasting-furnace, and after cooling the roasted material is itself passed through magnetic separators and the roasted chalcopyrite removed.

Having thus described my invention, What I claim is- 1. The method of treating ores containing non-magnetic or weakly-magnetic varieties of pyrrhotite, associated With chalcopyrite and gangue minerals, Which consists in heating the ore to a degree sufficient to make the pyrrhotite more magnetic than the chalcopyrite and Without considerable loss of sulfur, and subsequently removing the pyrrhotite from the other minerals by magnetic attraction; substantially as described.

2. The method of treating ores containing non-magnetic or Weakly-magnetic varieties of pyrrhotite, associated With chalcopyrite and gangue minerals, Which consists in heating the ore to such a degree that the particles of pyrrhotite shall acquire a surface iridescence or film of rainbow colors, and subsequently removing the pyrrhotite from the other minerals by magnetic attraction; substantially as described.

In testimony whereof I affix my signature in presence of tWo Witnesses.

JOHN N. JUDSON.

Witnesses:

I. Z. NOWLAN, J. J. MORRISON. 

